The inventor herein is also the inventor of several patents related to controlling a pellet mill, including U.S. Pat. Nos. 3,932,736; 4,340,937; and 4,463,430, as well as several patent applications, including Ser. No. 06/848,219 now U.S. Pat. No. 4,700,310, filed Apr. 4, 1986 and Ser. No. 06/907,232, filed Sept. 15, 1986, which are presently pending which further disclose and claim controllers and control modes for the pelleting process. The disclosures of these prior patents and applications are incorporated herein by reference. As detailed more fully and completely therein, various control algorithms have been previously developed which have been found to perform very satisfactorily in pelleting various formulations of material. The first of these developed is the so-called ".DELTA.T" control algorithm as is disclosed and claimed in U.S. Pat. No. 3,932,736. The basic concept of this control algorithm is that the temperature of the material is sensed at a first point prior to the addition of moisture and then at a second point after moisture has been added to the material and just prior to its entering the pellet producing means. The temperature differential between these two points is then determined and controlled as a means of producing pellets having a desired moisture content within a prescribed range. Still another control algorithm measures and controls the temperature differential across the pellet producing means and is commonly referred to as ".DELTA.T mill" as is disclosed and claimed in U.S. Pat. No. 4,340,937. Both of these control algorithms have met with tremendous acceptance and success in the industry and form the basis for automatic controls controlling many pelleting operations throughout the world.
Although both of these control algorithms have been previously developed and are in widespread use, there remains some minor difficulty in determining the exact temperature differential which should be utilized in any particular installation as well as with any particular type of feed. As can be appreciated by those of ordinary skill in the art, the amount of moisture in the material being fed to the pellet mill varies, as well as the die quality and the amount of wear previously experienced by the die as is evidenced in the amount of frictional energy generated in the mill which affects the temperature readings. Although measurements and calculations can be made to properly determine the temperature differential to be used with either of the control algorithms mentioned herein, this process does take some degree of sophistication and accurate measurement, and does represent a continuing need to rely upon the ability and skill of an operator.
One of the later developments of the inventor herein includes the concept of utilizing a non-contacting temperature probe to measure the temperature of the die as the pellet is formed, and the use of that single point temperature measurement to control the pelleting process. This development is the subject of several of the pending patent applications mentioned above and represents an exciting new advance by the inventor herein in developing still another control algorithm. As such, the single point non-contacting temperature probe or "pellet temp" control algorithm holds great promise for further sophistication in controlling the pelleting process. However, the inventor herein has found still another advantage to the non-contacting, single point die temperature probe in helping to solve the calculation and measurement problem previously experienced in determining proper temperature differentials for utilizing the .DELTA.T and .DELTA.T mill control modes. The inventor has found that by bringing the pellet mill up to temperature by measuring the temperature of the die until the die reaches the nominal change of phase point of water (boiling point), and at that point then measuring the temperature values at their appropriate locations, these temperature values can then be used to monitor and control the pellet mill in accordance with one of the prior control modes, i.e. .DELTA.T or .DELTA.T mill. Of course, this further automates the pelleting process in that it makes it possible for an operator to merely turn on the controller, and the controller can bring the pellet mill up to speed, monitor the temperature of the die, and at the point that the die reaches the pre-determined temperature measure the temperature at the other temperature sensors. The controller can then automatically use those measured temperature values as the desired values in continuing the pellet run under the .DELTA.T or .DELTA.T mill control algorithm. Thus, still another step in the process is removed from control of the operator and placed in the hands of automatic machinery to further mechanize and optimize the pelleting process. This method provides the further advantage of compensating for the idiosyncratic characteristics of the particular die, a parameter which is virtually impossible to independently determine, as well as the other more commonly determined values of moisture content of the material and ambient temperature.
The principal advantages and features of the invention have been briefly described. For a more thorough understanding of the invention, please refer to the drawing and description of the preferred embodiment which follows.